The present invention relates to a piezoelectric actuator, more precisely relates to a piezoelectric actuator capable of precisely positioning a magnetic head.
These days, capacity of magnetic disk units are made greater but size of them are made smaller. Therefore, memory density of magnetic disks are made greater. To make the memory density greater, number of tracks in a unit length (TPI) must be made greater. Namely, width of each track must be made narrower. To correctly read data from and write data in the narrow tracks, a magnetic head must be highly precisely positioned.
To precisely position the magnetic head, the inventors of the present invention tried to actuate an actuator arm by a head actuating mechanism, further they tried to slightly move the magnetic head or a head suspension so as to correctly position the magnetic head or the head suspension. The inventors found that deformation of piezoelectric elements and a specific structure of a carriage arm are capable of moving the head suspension and precisely positioning the magnetic head. The piezoelectric actuator of the present invention employs the deformation of the piezoelectric elements.
An exploded perspective view of a conventional piezoelectric actuator, which employs the deformation of the piezoelectric elements, is shown in FIG. 21. The piezoelectric actuator has a flat actuator base 10, which is connected to a carriage arm, and a hinge plate 14, which sandwich the piezoelectric elements 12 with the actuator base 10. A first electrode member 16 is provided between the actuator base 10 and the piezoelectric elements 12; a second electrode member 18 is provided between the piezoelectric elements 12 and the hinge plate 14. The electrode members 16 and 18 input electric voltage to the piezoelectric elements 12 so as to apply shear stress to the piezoelectric elements 12 and deform them.
The electrode members 16 and 18 input electric voltage to the piezoelectric elements 12 sandwiched between the actuator base 10 and the hinge plate 14, so the actuator base 10 and the first electrode member 16 are electrically insulated each other, and the hinge plate 14 and the second electrode member 18 are also electrically insulated each other. One side face of the first electrode member 16, which contacts the actuator base 10, is covered with an insulating layer; the other side face of the first electrode member 16, which contacts the piezoelectric elements 12, is covered with an electric conductive layer. One side face of the second electrode member 18, which contacts the hinge plate 14, is covered with an insulating layer; the other side face of the second electrode member 18, which contacts the piezoelectric elements 12, is covered with an electric conductive layer.
A plan view of a magnetic head assembly, to which the piezoelectric actuator shown in FIG. 22 is assembled, is shown in FIG. 21. The head suspension 20 is connected to the hinge plate 14. The deformation of the piezoelectric elements 12 move the hinge plate 14, in a plane, in the right-left directions, so that the head suspension 20 is also moved in the right-left directions and the magnetic head, which is mounted on the head suspension 20, can be correctly positioned. Side edges of the electrode members 16 and 18 are bent, and terminals 16a and 18a, which will be connected to a flexible printed circuit, are formed therein.
As shown in FIG. 22, in the magnetic head assembly including the conventional piezoelectric actuator, a terminal section 24, to which cables connecting to the magnetic head will be connected, is formed at one side edge of the head suspension 20; terminals 16a and 18a for actuating the piezoelectric elements 12 are formed at the other side edge thereof. With this structure, a flexible printed circuit, which will be connected to the terminal section 24 of the suspension 20, and another flexible printed circuit, which will be connected to the terminals 16a and 18a, must be required. Namely, manufacturing cost of the head assembly must be high. In the case that the terminal section 24 and the terminals 16a and 18a are provided on the same side of the head suspension 20 and one flexible printed circuit is connected thereto, positions of the terminal section 24 and the terminals 16a and 18a must be highly precisely located. If the are slightly shifted from the predetermined positions and a step-shaped section is formed between the terminal section 24 and the terminals 16a and 18a, it is very difficult to correctly connect the flexible printed circuit to the terminal section 24 and the terminals 16a and 18a, so that manufacturing cost of the head assembly must be higher.
In the conventional piezoelectric actuator shown in FIG. 21, the actuator base 10 and the hinge plate 14 are electrically insulated from the piezoelectric elements 12, and the electrode members 16 and 18 are provided between the actuator base 10 and the hinge plate 14 so as to input voltage to the piezoelectric elements 12. As described above, size of magnetic disk units are made smaller, so the piezoelectric actuator must be smaller and lighter. Mechanical characteristics of the piezoelectric actuator depends on its mass. If mass of the piezoelectric actuator is great, the carriage arm vibrates and badly influences the characteristics. Further, number of parts of the piezoelectric actuator must be reduced so as to reduce the manufacturing cost.
The present invention was invented to solve the disadvantages of the conventional piezoelectric actuator.
An object of the present invention is to provide a small and light piezoelectric actuator, which is capable of highly precisely positioning magnetic head assemblies, reducing number of parts and manufacturing cost, and improving characteristics.
To achieve the object, the present invention has following structures.
A first basic structure of the piezoelectric actuator of the present invention comprises: a movable member to which a head suspension is fixed; a fixed member being fixed to a carriage arm; a plurality of piezoelectric elements being provided between the movable member and the fixed member, the piezoelectric elements being capable of adjusting a position of the head suspension by their deformation; and an electrode member being provided to a part of the fixed member on which the piezoelectric elements are provided, the electrode member having an electric conductive layer, which is electrically insulated from the fixed member and electrically connected to one of electrodes of each of the piezoelectric elements, wherein the movable member is adhered on the piezoelectric elements and electrically insulated from the other electrodes of the piezoelectric elements, and the electric conductive layer of the electrode member and the other electrode of each of the piezoelectric elements are electrically connected to cables, which are provided to the head suspension so as to actuate the piezoelectric elements.
A second basic structure of the piezoelectric actuator comprises: a movable member to which a head suspension is fixed; a fixed member being fixed to a carriage arm; and a plurality of piezoelectric elements being provided between the movable member and the fixed member, the piezoelectric elements being capable of adjusting a position of the head suspension by their deformation, wherein the piezoelectric elements are fixed to the fixed member, and one of electrodes of each of the piezoelectric elements is electrically connected to the fixed member, the movable member is adhered on the piezoelectric elements and electrically insulated from the other electrodes of the piezoelectric elements, and the other electrode of each of the piezoelectric elements is electrically connected to a cable, which is provided to the head suspension so as to actuate the piezoelectric elements.
A third basic structure of the piezoelectric actuator comprises: a movable member to which a head suspension is fixed; a fixed member being fixed to a carriage arm; a plurality of piezoelectric elements being provided between the movable member and the fixed member, the piezoelectric elements being capable of adjusting a position of the head suspension by their deformation; and an electrode member being provided to a part of the fixed member on which the piezoelectric elements are provided, the electrode member having a pair of cable patterns, which are electrically insulated from the fixed member and electrically connected to electrodes of each of the piezoelectric elements so as to actuate the piezoelectric elements, and being extended so as to connect a flexible printed circuit thereto; wherein the piezoelectric elements are fixed to the electrode member, and one of the cable patterns is electrically connected to one of the electrodes of each of the piezoelectric elements, the movable member is adhered on the piezoelectric elements, and the movable member is electrically insulated from the other electrode of each of the piezoelectric elements, and the other cable pattern is electrically connected to the other electrode of each of the piezoelectric elements.
A fourth basic structure of the piezoelectric actuator comprises: a movable member to which a head suspension is fixed; a fixed member being fixed to a carriage arm; a plurality of piezoelectric elements being provided between the movable member and the fixed member, the piezoelectric elements being capable of adjusting a position of the head suspension by their deformation; a first electrode member being provided between the fixed member and the piezoelectric elements; and a second electrode member being provided between the movable member and the piezoelectric elements, wherein the first electrode member includes a pair of cable patterns, which are electrically connected to electrodes of each of the piezoelectric elements, and terminals, which are formed in a side edge of the fixed member and can be connected to a flexible printed circuit, and the second electrode includes a terminal, which is electrically connected to one of the cable patterns connected to one of the electrodes of each of the piezoelectric elements when the piezoelectric elements are sandwiched between the first electrode member and the second electrode member.
In the piezoelectric actuator of the present invention, the electrode member is provided between the fixed member and the piezoelectric elements or directly fixed to the fixed member, so number of the parts of the piezoelectric actuator can be reduced. By reducing the number of the parts, the piezoelectric actuator can be smaller in size and manufacturing cost can be reduced. If the terminal section includes the terminals of the cables for actuating the piezoelectric elements, a circuit connected to the piezoelectric actuator and the head suspension can be electrically connected by one flexible printed circuit, so that the structure of the piezoelectric actuator can be simple, the flexible printed circuit can be easily connected and the manufacturing cost can be further reduced.